This invention provides composite dental restorative compositions which are curable by the action of visible light. More particularly, formulations are disclosed which maintain good color stability and other beneficial physical properties while having the ease of workability and safety attendant to light curable materials.
Dental restoratives should exhibit certain obligatory physical and chemical characteristics in order to be suitable for use in filling, repairing or replacing teeth. Thus, restorative materials should possess properties that closely match natural teeth with respect to structural properties such as cohesive strength, coefficient of thermal expansion and wearability. Also, aesthetic considerations such as color stability, refractive index, plaque repellency, polishability and opacity are important factors in determining whether a material is suitable for use as a dental restorative. In the past, numerous organic compositions have been tried in various mixtures and proportions in order to find satisfactory materials for use as dental composites or restoratives. These compositions have usually included some type of resin, which may either be preblended or mixed by the practitioner in the office, together with other materials such as pigments, catalysts, handling agents and opacifiers. For restorative use, it is generally necessary to employ materials which are "filled", that is, to which have been added amounts of inorganic, or in some cases, organic particulate material.
Composite or restorative materials should be distinguished from most film forming dental compositions. Such film forming dental materials provide resins containing minor or no substantial amounts of filler materials. They are frequently used as sealants, glazes, bonding agents, or adhesives and may be used to coat a prepared tooth cavity prior to filling, thereby sealing off the tooth material against cracks and leaks adjacent to the filling. Such unfilled compositions have different viscosity requirements from dental composite materials because low viscosities are needed in the sealant materials in order to have proper flow characteristics. By contrast, dental composite and restorative materials must have good forming characteristics so that they can be shaped to fit a cavity area or molded into place in order to repair chipped or damaged teeth. Furthermore, such restorative compositions must preferably be filled with inorganic materials in order to achieve satisfactory hardness and durability during service.
It will be appreciated by those skilled in the art that the use of photoactivated materials is to be preferred over the more traditional thermochemical catalyst or redox activated systems because of the increased work time allowed by the use of photoinitiated polymerization. In a two-component catalyst or redox system, work time is determined by the reaction time once the catalyst is added to the resin component. In a photocured system, the practitioner may take whatever time is necessary for forming or molding the dental restoration into formation and then effect extremely rapid curing by exposing the photocurable material to the appropriate wavelength of electromagnetic radiation. Accordingly, effective aesthetically pleasing photochemically hardenable dental restorative compositions, have long been desired by those skilled in the art.
Some prior art dental materials have utilized photoinitiators that are sensitive to ultraviolet light radiation. There are, however, certain technical limitations which are present in ultraviolet-activated dental composite or restorative systems. For example, tooth structure attenuates ultraviolet radiation sufficiently so that it is not practical to cure ultraviolet-activated dental composites where direct access to the dental composite by the ultraviolet source is interfered with by intervening portions of tooth structure. Such is the case in classical undercuts used for mechanical retention of dental restorations. Ultraviolet-cured systems also cannot accomplish good depths of cure; stepwise restoration is frequently required.
It has been found that visible light having wavelengths from about 4000 angstroms to about 5000 angstroms is attenuated to a lesser degree by tooth structure than is ultraviolet radiation. Accordingly, it has been proposed to employ such visible light as the source of activating energy in dental compositions. Many previous attempts to develop restorative formulations using visible light curing systems have resulted in failure; such previous compositions have failed to exhibit one or more of the serviceability characteristics necessary for dental restoratives. A principal shortcoming is a lack of color stability and concomitant lack of aesthetic acceptability of the resulting products. Such a lack of color stability is a major shortcoming. The American Dental Association, the International Standards Organization, and others have developed detailed requirements for color stability in direct filling resins. See, for example, A.D.A. Specification No. 27; J.A.D.A. Vol. 94, June 1977, pp. 1191-1194.
Accordingly, it is a principal object of this invention to provide compositions which are useful as dental restoratives. It is another object to provide such dental materials which exhibit improved color stability. Another object of this invention is to provide a one-component photocurable dental restorative system which is photocurable using visible light. A further object is to provide dental compositions which exhibit a rapid cure time but which exhibit good workability prior to curing. Yet another object is to provide photocurable dental restoratives which are curable without use of ultraviolet radiation. A still further object is to provide dental compositions which are effective with lesser amounts of photoinitiators. Still other objects will become apparent from the following description of the invention.
It is to be understood that the term "bisphenol A" is commonly used in the art to indicate the chemical compound, 2,2-bis(4-hydroxyphenyl)propane. It is also to be understood that the term "bis-GMA" is commonly used to indicate the chemical compound 2,2-bis[4-(2-hydroxy-3-methylacryloxypropoxy)phenyl]-propane, otherwise referred to as "diglycidyl methacrylate of bisphenol A."
U.S. Pat. No. 3,825,518 to Foster et al. teaches dental filling materials which comprise a mixture of inorganic filler and the reaction product of an organic diisocyanate with a hydroxyalkyl acrylate or methacrylate to give a filled urethane diacrylate. A peroxide catalyst and a polymerization activator are employed.
U.S. Pat. No. 3,254,411 to Shelley teaches the use of a polyurethane liner to form a coating in the area of tooth to be filled. This liner acts as a sealant to prevent seepage of food particles and bacteria behind the filling that is to be placed in the tooth.
U.S. Pat. No. 3,488,269 to Allen et al teaches the use of visible light induced dye-redox initiated polymerization of vinyl monomers such as methacrylates. The improved initiators used here are characterized as having labile hydrogen.
U.S. Pat. No. 3,864,133 to Hisamatsu et al discloses photopolymerizable compositions which comprise a compound containing an ethylenically unsaturated double bond and urethane linkage and containing a secondary amino radical, a tertiary amino radical or a urea linkage. These materials are hardenable in the optional presence of air without the addition of wax. The materials formed are used in coating applications such as in wood sealers.
U.S. Pat. No. 3,759,809 to Carlick et al describes radiation curable compositions that have at least one isocyanate-modified polyfunctional ester with a hydroxyl value of about 15 to 70 used in conjunction with a photoinitiator. Reduced toxicity of these compounds is also noted. The primary use of these compounds is in lithographic inks.
U.S. Pat. No. 3,954,584 to Miyata et al. teaches that certain photopolymerizable vinylurethane monomers are useful in the preparation of printing plates and reliefs. Actinic light having wavelengths of from 2000 to 5000 angstroms may be used depending on the species of the photosensitizers used. Photopolymerizable vinylurethane monomers are used in conjunction with a photo co-polymerizable ethylenically unsaturated liquid monomer and a photosensitizer with the vinylurethane monomer.
U.S. Pat. No. 4,065,587 to Ting utilizes UV curable poly(ether-urethane)polyacrylates for the formation of wet-look polymers. U.S. Pat. No. 3,968,181 to Uzelmeier teaches modified photocurable acrylate resins including bis-GMA. A UV sensitizer such as a benzoin ether may be employed. These materials are useful as coatings and adhesives. U.S. Pat. No. 4,153,776 to Friedlander et al discloses amide-modified urethane acrylate radiation curable compounds which are useful in film applications.
U.S. Pat. No. 4,071,424 to Dart et al. teaches a photopolymerizable composition comprising at least one ethylenically unsaturated material and a photosensitive catalyst. Preferred photosensitizing systems employ alpha diketones with an amine reducing agent capable of being excited by radiation in the visible as well as in the UV region or both.
U.S. Pat. No. 4,089,762 to Frodsham teaches the use of a photopolymerizable composition comprising a polymerizable ethylenically unsaturated material, a photosensitizer of the structure which is preferably a diketone and a N-alkyl or N-cycloalkyl morpholine.
U.S. Pat. No. 4,089,763 to Dart et al teaches a method of repairing teeth using a composition which is curable by irradiation with visible light. These compositions include isocyanate modified bisphenol A derivatives in conjunction with a visible light sensitizing system.
U.S. Pat. No. 3,709,866 to Waller, assigned to the assignee of this invention, discloses the hexamethylene diisocyanate adduct of bis-GMA in a UV photocurable system. Benzoin methyl ether is employed as a UV activator. This disclosure is in part reflected in the commercial products NUVA-FIL, and NUVA-FIL P.A., which are registered trademarks for products past or present of the L. D. Caulk Co.
U.S. Pat. Nos. 4,227,979 issued to Humke et. al., 3,625,744 issued to Juna et. al, and 4,077,859 issued to Costanza are each directed to radiation curable coating compositions.
British Pat. No. 569,974 issued to DuPont discloses photopolymerizable dental compositions comprising polymer-monomer mixtures. Dental restoratives having major proportions of inorganic fillers are not suggested thereby.
U.S. Pat. No. 4,292,029 issued to Craig et. al. is directed to hydrophobic dental composite restorations. The possibility of visible light curable one-phase systems is suggested.
None of the the foregoing disclose or suggest the novel methods and compositions of the present invention.